Abstract
The epicardial depolarization wave forms of both ventricles were examined to ascertain the local depolarization process at the stimulating site. Twenty-one mongrel dogs were used, and their hearts were exposed to the air through midsternal thoracotomy under artificial respiration. A single Ag/AgCl electrode was used. This electrode was nonpolarizable and its shape was spherical, 2 mm in diameter. It was attached to the heart by means of cyanoacrylate adhesives so that the electrode could contact the myocardium with constant pressure.
Epicardial stimulation and epicardial potential recording could be carried out simultaneously by this electrode.
In the early phase of the depolarization, the wave showed a negative plateau potential of -47.5±9.4mV (mean±SD) for the left ventricle and -40.1±8.6mV for the right ventricle. A difference in plateau potential was recognized between the two ventricles, and it was considered to be related not to wall thickness, but to electrical and morphological characteristics of the myocardial cell. The duration of this plateau potential was 32.9±4.6msec for the left ventricle and 18.3±3.7msec for the right ventricle. A simple model was introduced in which the excitation wave front was considered to be a single dipole layer and to propagate hemispherically or hemiellipsoidally. The potential induced at the center of the hemisphere was estimated from the model to be constant at about -50mV, as far as the wave front fromed a closed surface until it reached the electrical boundary of the ventricular wall. It was thought that wall thickness and conduction velocity must be responsible for the plateau duration.
